1. Technical Field
The present disclosure relates to a direct current (DC) circuit breaker and a method using the same. More specifically, the present disclosure relates to a DC circuit breaker for quickly and efficiently interrupting a high-voltage direct-current (HVDC) system for protecting devices as well as the system at the time of maintenance or replacement of a device, or when a fault-current occurs in a transmission line or a distribution line of the system. The present disclosure also relates to a method using the same.
2. Description of the Related Art
In general, a DC circuit breaker is used for quickly and efficiently interrupting a high-voltage direct-current (HVDC) system for protecting devices as well as the system at the time of maintenance or replacement of a device, or when a fault-current occurs in a transmission line or a distribution line of the system.
Recently, a DC circuit breaker tends to be designed with power semiconductor switches which have a shorter response time and are less likely to damage adjacent lines when a fault occurs. Unfortunately, such a DC circuit breaker employing power semiconductor switches suffers a large electrical current loss, and thus is not appropriate for HVDC transmission. Specifically, a large number of power semiconductor switches, e.g., about tens to hundreds power semiconductor switches are required to conduct HVDC transmission. In addition, such a large number of power semiconductor switches result in electrical current loss.
There has been proposed an approach to improve such shortcoming, which is shown in FIGS. 1 and 2. The approach will be described with reference to FIGS. 1 and 2.
FIG. 1 shows a base element 6 for the solid-state circuit breakers disclosed in the reference. The solid-state circuit breakers are main and auxiliary circuit breakers which will be further described below. The base element 6 includes a power semiconductor switch 1 disposed in a first current direction 4 and a free-wheeling diode 2 connected in anti-parallel to the power semiconductor switch 1.
The base element 6 is used in an example of a device depicted in FIG. 2. A circuit breaker 13 is connected in series with a transmission line 14 as shown in FIG. 2. The transmission line 14 is HVDC transmission line. The circuit breaker 13 includes a main circuit breaker 8 including: tens to hundreds of, depending on a voltage level, the base elements 6 connected in series; a non-linear resistor 11 connected in parallel to the main circuit breaker 8; and a high-speed switch 10 and an auxiliary circuit breaker 9 connected in series, which are connected in parallel to the main circuit breaker 8 and the non-linear resistor 11. The auxiliary circuit breaker 9 includes only one base element 6. Although the high-speed switch 10 is shown as one mechanical switch, which includes at least two mechanical switches that are connected in series and operated simultaneously. A reactor 12 is connected in series to the circuit breaker 13 to limit a current rating.
Operation of the circuit breaker 13 disclosed in the reference is as follows.
During a rated current operation, the high-speed switch 10 is closed as well as the main circuit breaker 8 and the auxiliary circuit breaker 9, so that the rated current flows through the high-speed switch 10 and the auxiliary circuit breaker 9.
When a fault-current is caused by a defect occurring on a line, the auxiliary circuit breaker 9 is opened immediately within a few microseconds after receiving an auxiliary circuit breaker opening signal, causing the fault-current to flow to the main circuit breaker 8. The high speed switch 10 waits for a while to make it sure that the auxiliary circuit breaker 9 is opened, and then is opened. After the opening of the high-speed switch 10 is opened, the main circuit breaker 8 is opened immediately within a few microseconds. When the main circuit breaker 8 is opened, the fault-current is led to flow to the non-linear resistor 11, and then a current level is reduced and a voltage is limited.
However, the main circuit breaker 8 in the reference requires several tens to hundreds of power semiconductor switches connected in series for use in a HVDC system operated in several hundred kV. Since the power semiconductor switches are expensive, manufacturing cost of the DC circuit breaker increase.